Automatic press control system



Patented July 2 9, 1941 AUTOMATIC PRESS QONTROL SYSTEM Walter Ernst,Mount .Gilead, Ohio, assignor to The Hydraulic Development Corp. Inc.,Wilmington, Del., a corporation of Delaware Application August 31, 1939,Serial No. 292,932

2 Claims.

This invention relates to presses, and in particular, to control systemsfor hydraulic presses.

a One object of this invention is to provide an automatic. press controlsystem, wherein the press ram-is. halted at the end of its workingstrokeand held in its halted position for a predetermined period of timebeforebeing automatically reversed and retracted. I

Another object is to provide an automatic press control system, whereinthe press ram is halted at a predetermined point on its forward strokeby tripping a limit switch which sets in motion a time delay deviceadapted to alter the energization of the electrical press controlcircuit at the end of the period of time for which the device isadjusted, thereby reversing and retracting the press ram.

Another object is to provide an electrical press control system,-wherein the press ram is halted and held under a predetermined pressureat a predetermined position on its forward stroke for a predeterminedperiod of time as controlled by a time delay device, after which thepressure is-automatically released and pressure fluid admitted to thepush-back cylinders to retract the press ram.

The drawing shows one embodiment of a press having an automatic controlsystem according to the invention, arranged in a diagrammatic circuitpartly in section.

In general, the automatic press control system of this inventionconsists of a limit switch adapted to be shifted by the press ram at aposition corresponding to the end'of its working stroke, but reversal isdelayed by the action of a time delay device. at the end of the workingstroke, pressure is During the dwell thus providedthe invention, inbrief, includes a pressurere sponsive switch actuated by the control rodof v the press at the limit of the working stroke, with a time delaydevice to provide a dwell and to prevent premature backing off of thepress ram, a pressure-holding servomotor being provided with areversible variabledelivery pump to prevent a continuing rise ofpressure during the time delay period. The particular arrangement shownin the drawing also utilizes a closed hydraulic circuit interconnectingthe pump and press.

Referring to the drawing in detail, there is shown a press III, areversible variable delivery main pump ll of the pressure-holdingservomoa fluid tank l3, a pilot pump l4, a control valve I5,,a timedelay device IS, a solenoid H for. ac-

gization of the solenoid H, a press-reversing maintained upon theworkpiece at a predeterdelivery position, causing pressure fluid to. be

supplied to the push-back cylinders and withdrawn from the maincylinder, thereby retracting the press ram. When the press ram reachesthe end of its return or retraction stroke, an arm attached to the ramactuates mechanism which places the pump flow-control member or shiftring in its neutral position and thus holds the press ram in itsretracted location.

Thus the automatic press control system of bed 2!.

arm 29 for engaging a stop collar 30 upon the limit switch l9 forinitiating the operation of the time delay device [6 and a push-buttonswitch 20 for initiating the operation of the entire circuit.

The push-button switch 20 is provided as the simplest form of startingarrangement to furnish semi-automatic operation. -It will be evidentthat the circuit may beenlarged to provide full automatic operation bycircuits known to those skilled in the art.

The press i0 is shown diagrammatically for the sake of simplicity, andconsists of a. bed 2| connected by strain rods 22 to a head 23. Mountedon the head 23 is a main cylinder 24 containing a main plunger 25, towhich is attached the press ram or platen 26. Also secured to the latterare push-back plungers Z'l reciprocating in push-back cylinders 28mounted upon .the press The press ram 26 is provided with an presscontrol rod 3!, the latter being reclprocably supported by the arm 32mounted upon the press bed 2|. The control rod 3! is urged upwardly bythe compression spring 33, mounted between the collar 30 and the end ofthe arm 32..

The control rod 3| also carries anannular cam 36 near its lower end forclosing the normally open reversing limit switch IS. The latter isprovided with a switch arm 35 and contacts 36 and 31, maintained in anormally open condition by the coil spring 38. The control rod 3| alsocarries a collar or head 39 at its upper end,

beneath which is a coil spring 40 providing a a cushioning stop for theplaten arm 29. Separable from the control rod 3| but in contactingengagement therewith is the valve-lifting rod 4| of the valve I5. Thelatter serves to lift the valve plunger 42 when the platen arm engagesthe coil spring 40 and lifts the control rod 3| and valve-lifting rod 4|into the position shown in the drawing. A coil spring 43 urges the valveplunger 42 downwardly toward its seat 44 between the inlet chamber 45and exhaust chamber 45. The latter is connected by the exhaust conduit41 to the tank I3, whereas the former is connected by the by-passconduit 48 with the pilot pump I4.

' The valve I also contains a pressure relief plunger 49, urgeddownwardly by a coil spring 50 to close the passageway 5| leading fromthe conduit 48 to the chamber 52. The latter is connected by thepassageway 53 to the exhaust chamber. Thus when pressure in the conduit48 exceeds a predetermined maximum, it raises the pressure relief valveplunger 49 and escapes through the chamber 52, the passageway 53, theexhaust chamber 45 and the exhaust conduit 41, back to the tank I3. Thevalve-lifting rod 4| is provided with spaced collars 54 engaged by theyoked end of a lever 55, pivotally mounted upon the shaft 56 andpivotally connected to the armature 51 of the solenoid I1. The armature51 is urged upwardly by the compression spring The main cylinder 24 issupplied with pressure fluid from the main pump H by way of the conduit59, having a branch 65 communicating with a chamber 5| surrounding thepump centering piston area 62 upon the pump flow-control rod 63. Thelatter is connected to the shift ring of the reversible variabledelivery pump II, the

conduit 18 to the conduit 59, whereas the opposite end chamber 11 isconnected by the conduit 19 with the conduit 12.

In addition to the press reversing limit switch I9 and the solenoid I1,the electrical circuit contains the time delay device I6 and thecontactor I8, all of which are energized from the power lines 80 and 8|.The power lines 80 and 8| are connected to the lines 82 and 83 leadingto the solenoid winding 84 when the contactor coil 85 is energized so asto pull its armature 86 to the left and with it the switch blades 81, 88and 89 into engagement with their respective contacts. The coil spring90 holds the armature B5 and switch blades 81, 88. and 89 in a normallyopen condition when the contactor coil 85 is deenergized.

' The switch blade 59 provides a holding circuit for maintaining theenergization of the contactor coil 85 by way of the power line 8|, thelines 9|,92, 93 and 94, the contacts 95 and 96 of the time delay deviceI5, and the line 91 leading to the power line Bil. This holding circuitis main- 1 tained after the circuit between the lines 98 and the circuitin operation. The press-reversing opposite side of which is connected tothe rod I 64, threaded as at 65, to receive a hand wheel 55 foradjusting the thrust of a coil spring 51 mounted within the cylindricalspring casing 58. The spring 61 urges the shift ring of the pump in onedirection in opposition to the pressure of the pressure fluid againstthe centering piston area 62. When the pressure in the main cylinder 24rises to a sufiicient height to overcome the thrust of the spring 61, itpulls the shift ring of the pump II to its neutral or no-deliveryposition. The pump II is of the radial piston type, well known to thoseskilled in the art.

The pump flow-control rod 63 beyond the centering piston area 62 isprovided with an enlarged piston head 69, reciprocable within 3.cylinder 1B supplied with pressure fluid on its left hand side by theconduit 1| connected to the pilot pump pressure conduit 48. Whenpressure limit switch I9 is connected to the time delay device Is by theline 99, and to the power line 8| by the line I00. The time delay deviceI6 is provided with a motor IIlI which opens the contacts 95 and 95 apredetermined period of time after the energization of the motor IIlI,in a manner well known to those skilled in the art.

In the operation of the press control system of this invention, to startthe press in operation the operator momentarily depresses thepush-button switch 29. This action energizes the coil 85 of thecontactor I8, causing the armature 86 to move to the left so that theswitch blades 81, 88 and 89 engage their respective contacts. Theenergization is maintained through the holding circuit established bythe switch blade 89, in the manner previously described. The consequentenergization of the winding 84 of the solenoid I1 pulls the armature 51downward, and rocks the lever so as to push the valve-lifting rod 4|fluid of a sufliciently high pressure is admitted through the conduit 1|to the inner end of the cylinder 10, it shifts the piston head 69 andpump flow-control rod 53 to the right, placing the shift ring of thepump in its reverse position so' that pressure fluid is thenceforthdischarged through the conduit 12 leading to the push-back cylinders 28.At the same time, in its reversed condition the pump II withdraws fluidfrom the main cylinder 24, through the conduit 59, as hereinafterdescribed in connection with the operation of the circuit. The tank I3is connected by a conduit 13 with the middle chamber 14 of the make-upvalve I2, the valve member 15 of -which is shifted to and fro bypressure existing in the conduit 12 or the conduit 59 so as to upwardsAssuming that the main pump II and pilot pump I4 are running, theunseating of the valve plunger 42 by this operation causes the dischargeof the pilot pump I4 to be by-passed through the line 48, the chambers45 and 46 and the conduit 41, to the tank I3. Thus no pressure ispermitted to stand in the left-hand end of the pumpreversing cylinder10, and the spring 61 consequently urges the rod 64 and pump shift ringto the left, placing the pump II upon stroke in a forward deliveryposition. When this occurs the pump I I delivers pressure fluid throughthe conduit 59 to the main cylinder, 24. forcing the main plunger 25 andpress ram or platen 25 downwardly. At the same time fluid is withdrawn Afrom the pull-back cylinders 28 through the con- The ram 25 descendsuntil it reaches while, the pressure built up in the main cylinder bythe resistance of the workpiece backs up in the conduits 59 and 60 andchamber Bl, where it acts against the centering piston area 82 toovercome the thrust of the coil spring 61 and pull the pump flow-controlrod 63 and shiitring to their neutral position. The pump H then holdsthe pressure upon the main plunger 25 at a predetermined maximum,depending upon the thrust of the spring 61 as adjusted by the hand wheel66.

When the timing motor Hil has run the course for which it has been set,it separates the contacts 95 and 96, breaking the circuit between thelines 91 and 94 and deenergizing the coil 85 of the contactor IS. Thelatter then opens, deenergizing the winding 84 of the solenoid ii.

The coil spring 43, which has been compressed,

by the energization of the solenoid l'i, now pushes the valve plunger 42downward into engagement with its seat, closing of! communicationbetween the chambers 46 and 45 and ending the by-passing of the pilotpump l4 through the' conduits 4B and 41. The pilot pump It then deliverspressure fluid through the line 1| into the left-hand end of thepump-reversing cylin- .1

der HI, causing the large piston head 69 to overcome the thrust of thecoil spring 61 and shift the pump flow-control rod 63 and shift ringpast their neutral positions into their reversed positions. The pump ll,thus reversed, discharges pressure fluid into the conduit 12 andpush-back cylinders 28, forcing the push-back plungers 21,

main ram 28 and main plunger 25 upward upon their retraction or returnstrokes. At the same time the pump ll withdraws fluid from the maincylinder 24 by way-of the conduit 59.

When the main ram or platen 26 nears the end of its return or retractionstroke the arm 29 engages the coil spring 40 and lifts the control rod3| by means of its head 39. This forces the valve-lifting plunger 4|upward a short distance so that it lifts the valve plunger 42 slightlyon its seat 54. This action permits the pressure in the conduit H to berelieved-slightly by a slight by-passing through the conduits 48 and 41,thus permitting the pump flow-control rod 63 and shift ring to return totheir neutral or no-delivery positions. When the platen 26 tends todescend, however, the platen arm 2! releases the coil 'spring 40 andpermits the control rod 3i, valvelifting plunger 4| and valve plunger 42to descend,

ending the by-passing' action and permitting the pressure to be raisedby the pilot pump l4 inthe conduit "II and reversing cylinder 10. Inthis manner the shift ring of the pump H is mainthe end of itsretraction stroke, and the main ram 26 is held in its raised positionand prevented from coasting downwardly.

It will be understood that I desire to comprehend within my inventionsuch modifications as come within the scope of the claims and theinvention.

Having thus fully described my invention, what I claim as new and desireto secure by Letters Patent is:

1. A hydraulic press control system comprising in combination, a liquidoperable and reciprocable main plunger, a reversible pump for supplyingpressure fluid to actuate said main plunger in opposite directions, a.pilot pump feeding a hydraulic circuit for reversing said reversiblepump, valve means controlling the supply of liquid from said pilot pumpto said reversing circuit, means normally biasing said valve meansintoone position, a press control element comprising two axially alignedunconnected parts mounted for movement parallel to said main plunger, anelectric operator having means connecting the same to the first of saidparts whereby .energization of said electric operator will operate saidfirst part, said valve being connected to the first of said parts andadapted to be actuated thereby against said biasing means, means on saidsecond part whereby the same may be actuated by said main plunger duringpart of its movement in one direction, bothof said parts being actuatedin the same direction by said main plunger and said electrical operator,additional means on said second part whereby actuation by saidsecondpart, when the same is moved by said additional means, and meansactuated by said switch for de-energizing said electric operator wherebysaid biasing means moves said valve means to reverse said reversiblepump and cause the retraction of said main plunger.

2. The combination as claimed in claim 1 including a timing deviceadapted to be energized by the operation of said electric switch fordelaying de-energization of said electric operator for a predeterminedperiod of time.

WALTER ERNST.

